1. Introduction

In this tutorial, our primary goal is to acquaint you with the basics of creating and using JavaScript functions. JavaScript functions are the fundamental building blocks of JavaScript programming. They help in structuring the code, making it reusable and maintainable.

You will learn:
- What JavaScript functions are
- How to create and use JavaScript functions
- Best practices when working with JavaScript functions

Prerequisites:
Basic understanding of JavaScript syntax and programming concepts.

2. Step-by-Step Guide

JavaScript functions are blocks of code designed to perform a particular task. They are executed when they are called (or 'invoked').

Here's the basic syntax of a JavaScript function:

function functionName() {
  // code to be executed
}

Tips:
- Function names are case-sensitive and can contain letters, digits, underscores, and dollar signs.
- The code inside the function will execute when "something" invokes (calls) the function.

3. Code Examples

Example 1: Creating a Simple Function

// Function declaration
function greet() {
  console.log("Hello, world!");
}

// Function invocation
greet();

In this example, greet is the function name, and the code inside the {} is the function body. console.log("Hello, world!") is the task that the function will perform. The function is invoked by writing the function name followed by parentheses (). The output of this code will be Hello, world!.

Example 2: Function with Parameters

Functions can also take parameters.

// Function declaration
function greet(name) {
  console.log("Hello, " + name + "!");
}

// Function invocation
greet("Alice");

In this example, name is a parameter. When we invoke the function, we pass an argument "Alice", which replaces the parameter name within the function body. The output of this code will be Hello, Alice!.

4. Summary

In this tutorial, you have learned the basics of JavaScript functions, including how to declare, define, and call them. You've also learned how to pass parameters to a function.

The next step is to learn about function return values, anonymous functions, and arrow functions. For more detailed information, visit Mozilla Developer Network.

5. Practice Exercises

Exercise 1: Write a function that multiplies two numbers and logs the result.

Solution:

// Function declaration
function multiply(num1, num2) {
  console.log(num1 * num2);
}

// Function invocation
multiply(5, 4);

This function multiplies num1 and num2 (5 and 4 in this case) and logs the result. The output will be 20.

Exercise 2: Write a function that accepts a name and a favorite color and logs a personalized greeting.

Solution:

// Function declaration
function personalizedGreeting(name, color) {
  console.log("Hello, " + name + "! Your favorite color is " + color + ".");
}

// Function invocation
personalizedGreeting("Bob", "blue");

This function takes name and color as parameters and logs a personalized greeting. The output will be Hello, Bob! Your favorite color is blue..

To further practice, try creating functions that solve different problems, use different parameters, and perform different tasks. Happy coding!